Analysis of Gas Content and Permeability Change Pattern of a Coal Reservoir in the Tectonic Positions Based on a THM Coupled Model

Table 2

Basic types of structures controlling gas content in the Guojiahe wellfield.

Structure type	Structure parts	Gas distribution characteristics
Gentle dip syncline	Shallow buried part of syncline limbs	(i) Shallow parts of both limbs are not conducive to the preservation of CBM; (ii) Axial part of the syncline better than both limbs; (iii) Syncline upwarping part CBM enrichment; (iv) The CBM in the intersection of the main dip fold axis and the larger secondary syncline is better endowed
	Axial part of the syncline
	Syncline upwarping part
	Intersection part of the syncline and secondary syncline
Anticline and secondary anticline	Axial part of anticline	(i) Low gas content in the main anticline due to the coal erosion.; (ii) The secondary anticline is rich in CBM, the tensional fracture is developed on both limbs, the coal cover is closed, and the gas content is high on both limbs
	Secondary anticline with normal faults
Normal fault	/	(i) Tensional fractures with poor sealing of faults contribute to the migration or escape of CBM